standard input

Abbrevitaed as stdin, standard input is information inputted into the terminal through the keyboard or input device.

standard output

Abbreviated as stdout, standard output is the information outputted after a process is run.

standard error

Abbreviated as stderr, standard error is an error message outputted by a failed process.

For example, below, the echo command accepts the string Hello as standard input and echoes the string Hello back to the terminal as standard output.

$echo "Hello"

Hello